1. Field of the Invention
The present invention relates to sterilizing and disinfecting solutions containing glutaraldehyde as the active ingredient. The present solutions contain an improved buffering composition. The solutions of the present invention are capable of being diluted with hard water without becoming turbid and without any reduction in the efficacy of the solution as a sterilizing or disinfecting solution.
2. Prior Art
Glutaraldehyde solutions are well known as sterilizing and disinfecting agents. These solutions are buffered to maintain the solution at a specific pH range during use. The following United States patents disclose such solutions and various compositions used as the buffering agent.
1. Pepper et al. U.S. Pat. No. 3,016,328, which teaches disinfecting with a sporicidal composition containing saturated dialdehyde, such as glutaraldehyde, and an alkalinating or buffering agent in either an alcoholic solution, or an aqueous solution at above pH 7.4. The alkalinating or buffering agent is an alkali metal carbonate or bicarbonate.
2. Stonehill U.S. Pat. No. 3,282,775, which teaches disinfecting with sporicidal solutions containing a saturated dialdehyde, preferably glutaraldehyde, and a cationic surface active agent. The solutions are buffered with alkali metal carbonates, bicarbonates, phosphates, borates or certain amines such as diethylaminoethanol and dibutylamine.
3. Winicov et al. U.S. Pat. Nos. 4,048,336 and 4,093,744, which teach sporicidal solutions containing glutaraldehyde at pH 6.5 to pH 7.4, which may contain a detergent and also a monoaldehyde. The activator or buffer may be phosphates, citrates, carbonates or bicarbonates.
4. Buchalter U.S. Pat. No. 3,983,252, which teaches disinfectant solutions that contain a dialdehyde in an aqueous solution buffered with an alkali metal salt of a hydrocarbon carboxylic acid in aqueous solution. The solution also contains an alcohol, diol or triol. The compositions are stated to have improved stability in the pH range of from 6.0 to 7.4.
Generally, aqueous glutaraldehyde solutions are stable almost indefinitely within a pH range of 2.5 to 4.5. However, at an acidic pH, glutaraldehyde solutions exhibit poor sporicidal activity. Just prior to use, pH levels of the glutaraldehyde solutions are adjusted through the addition of an alkalinating or activating agent which is the buffering composition for the solution. The addition of the activating agent increases the pH level to above 7 where these compositions have greater sporicidal activity. The normal buffering agents employed are generally inorganic salts such as phosphates, citrates, carbonates or bicarbonates. The commercial solutions are usually packaged with the aqueous glutaraldehyde solution at a pH in the acid range and the activator packaged in a separate container and added to the solution immediately prior to use. When used as a sterilizing composition, the concentration of the glutaraldehyde is normally in the range of 2% to 4% by weight with the remainder of the solution being generally deionized water. When used as an environmental surface disinfectant, the concentration of the glutaraldehyde in the solution may be as low as 0.05%. It has not heretofore been found practical to ship concentrated glutaraldehyde solutions, i.e., 10% to 25% glutaraldehyde, to be diluted at the point of use with tap water because of the variation in the quality of the tap water. The hardness of the tap water causes problems with the buffering or activator compositions for the solutions. In very hard water, the normal phosphate type activators will react with calcium and magnesium salts in the tap water to form an insoluble precipitate. This insoluble precipitate causes the active solutions to become turbid and the precipitate may deposit on the surgical instruments which are sterilized by the compositions.
Although it is known that borate salts will not form precipitates with the calcium and magnesium ions found in hard water, the borates have not been found acceptable as the activating composition in glutaraldehyde sterilizing and disinfecting solutions because they have an adverse effect on the biological activity of the solutions in use. That is, a glutaraldehyde solution with a borate activating composition is not as effective in terms of its sporicidal activity as a glutaraldehyde solution activated with a phosphate activator composition. It is also known that chelating agents, such as ethylenediaminetetraacetic acid, will prevent precipitate formation with hard water. However, aqueous glutaraldehyde solutions containing these compounds are corrosive to certain metals used in medical instruments and equipment.
In addition to the problems of intentional dilution with tap water mentioned above, glutaraldehyde solutions are often unintentionally diluted with tap water during use. The unintentional dilution results from the contamination of the solution with rinse water during the normal use of the solution. If the water used for the rinse water has any significant hardness, i.e., 50 ppm or higher, inorganic phosphate buffers in the solution can combine with the calcium and magnesium ions in the water and form an insoluble salt which will precipitate on the devices being sterilized. The reduction in the phosphate ion concentration in the solution may also reduce the sporicidal activity of the solution.